In today's urban environments, many people live or work in multi-storied buildings such as sky-scrapers. In case of a fire or terrorist attack, rapid descent from upper floors of such buildings may be necessary. In such emergency situations, use of an elevator may be unsafe. Emergency stairwells may become blocked by fire or smoke, making rapid escape difficult. Descent devices may be used in such emergency situations to allow a rescuee to be safely lowered to the ground.
A serious concern in Controlled Descent Device (CDD) design involves prevention of suspension trauma which may occur if the rescuee remains suspended in a safety harness after an arrested fall. Suspension trauma may cause serious injuries and even death, due to interruption of blood flow to and from the lower extremities of the rescuee's body caused by pressure applied by the leg straps over the arteries and veins of the upper leg and groin region of the rescuee.
Some controlled descent devices known from the patent literature are briefly described below.
U.S. Pat. No. 3,760,901 describes a lifesaving system for escaping from high buildings using a descending bar coupled to the upper part of a window and which projects outwardly, or is coupled to a fixed point of a place a user wishes to escape the building from. A harness or belt snugly surrounds a part of the body of the user, and a hermetically closed element, that has an assembly of wheels coupled to each other in its interior, is joined by a part to the harness or belt, and therefore to the user, and is also joined by another part, such as a hook, to the descending bar when the user to be rescued leaves the building by descending vertically.
US Patent publication No. 2004245048 describes a rappelling device for permitting persons to be rescued from high buildings, towers, and the like, having a suspension strap, suspension vest, or the like, to be worn by the person in question, wherein a rope container having a device to release the rope length is provided on the suspension strap, which solution is supposed to be easy to operate, on the one hand, and to be made available to the persons in question at any time, and easy to handle for them, whereby the person using the device can essentially move both hands freely, in a stable rappelling position. This is achieved in that the rope drum that forms the rope container, in the wearing position on the back of the person using the device, is provided with a rope guide device for passing the rope to a release position in the chest region of the person using the device.
International Patent Publication No. WO 03/055560 discloses an abseiling device used as rescue equipment in disaster situations, particularly fires in buildings or tall buildings, comprising a harness for supporting particularly a person, a housing provided with a rope drum and an automatic braking device, and a rope, one end of which is fixed to the building and the other end of which is fixed to the housing. The housing is connected to the harness so as to form a unit.
U.S. Pat. No. 4,063,615 describes an escape device which includes a housing from which the user of the device is supported. The housing journals a drum about which a cable is coiled. During use of the device the free end of the cable is secured to a building part while the user being supported by the housing descends to the ground. A braking mechanism is incorporated in the housing to regulate the rate of descent of the housing and supported user.
US Patent No. US 2010/122874 describes a self-rescue system and a method for providing self-rescue to fall-victims suspended in fall-arresting safety harnesses following an accidental fall enables such suspended fall victims to descend to the ground or other place of safety at a controlled, safe velocity, without assistance from anyone else. In addition, the invention can also address applications in many types of elevated locations where a controlled descent is needed in order to escape emergency conditions.